1. Field of the Invention
The invention generally relates to a fuel cell system including a hydrogen tank for supplying hydrogen gas and a fuel cell for receiving the hydrogen gas and generating electric power, a method of controlling the system, and a vehicle mounted with the system. More particularly, the invention relates to a fuel cell system capable of controlling the temperature of a fuel cell, a method of controlling the system, and a vehicle mounted with the system.
2. Description of the Related Art
When a vehicle with a fuel cell system including both a high-pressure hydrogen tank and a fuel cell is used in, e.g., a cold region in winter, the ambient temperature is so low (e.g., below 0° C.) that the fuel cell (e.g., electrolyte membranes therein) may possibly be in a frozen state before the fuel cell system is started. The fuel cell cannot be operated in such a state. Accordingly, when the fuel cell system is to be started, the fuel cell can be operated only after thawing the fuel cell, i.e., after heating the fuel cell to normal temperature (e.g., 0° C. or higher).
In such a case, the related art employs a method of heating the fuel cell or the cooling water circulating therein by using an electric heater or a combustion heater.
The related art also employs the same method in the case where the temperature of the fuel cell does not rise to a proper temperature even after the fuel cell has begun operation.
For example, the method using the electric heater requires a large-capacity battery to be mounted on the vehicle in order to supply electric power to the electric heater.
In the method using the combustion heater, hydrogen gas (i.e., fuel to be supplied to the fuel cell) is supplied to the combustion heater and burnt therein. Accordingly, the fuel (hydrogen gas) thus supplied to the combustion heater is used only for combustion, not at all for generation of electric power in the fuel cell. This is a loss of energy from the standpoint of power generation. Note that even the method using the electric heater is subjected to the same problem if electric power generated by the fuel cell is accumulated in the battery for use in heating the electric heater.
It is also possible to entirely wrap the fuel cell in a heat insulating material to keep the fuel cell warm. In this method, however, the fuel cell can be kept at a proper temperature for a certain time after operation of the fuel cell is terminated, but the temperature of the fuel cell falls to the ambient temperature over time. Therefore, the fuel cell must still be heated to a proper temperature upon starting of the fuel cell system after a long interval of non-use.